The use of forms, casings, moulds and shells is well known in the construction of cast-in-place concrete footings, piers and piles. These footings, piers and piles are used to transfer the loads of buildings, bridges, decks, porches, raised walkways, ramps, mini-home supports, highway sign posts and add-ons of existing structures to the underlying supporting soil. The concrete of a cast-in-place pile or footing is cast inside a mould that usually consists of a tin metal, plastic or paper shell left in the ground. The mould is usually so thin that its strength is disregarded in evaluating the structural capacity of the pile or footing. However, the mould must have adequate strength to resist collapse under the pressure from the surrounding backfill before it is filled with concrete. Similarly, if the mould is filled with concrete without the support of backfill, the mould must have sufficient strength to resist bursting pressures.
In northern latitudes, such as those which encompass Canada, northern Europe and the northern portions of the United States, soils, and particularly fine grained water saturated soils, are susceptible to the formation of ice lenses and frost heave. These phenomena can greatly diminish the stability and integrity of structures embedded in such soils. Therefore, footings are placed at a depth of not less than the depth of normal frost penetration. This prevents damage to the footing from the swelling and shrinkage of the surrounding soil caused by freeze-thaw cycles or displacement from frost heaving. However, while placing the footing below the depth of frost penetration will protect the footing from the effects of frost action, the pier that transfers the loads from the supported structure to the footing remains above the frost line and therefore remains vulnerable to frost and ice action.
The mechanisms of frost heave and frost action are well known to persons skilled in the art. The main phenomenon of concern to the construction industry is the displacement, laterally and vertically, of foundation members due to loads placed upon them from frost action. Where surrounding soil is frozen to a pier connecting a supported structure to a supporting footing, movement of the soil frozen to the pier will displace the pier. This will diminish the stability of the footing and structure to which it is attached no matter the depth of the footing below the frost line. In northern climates, a pier must be of a significant length to connect a footing placed below the frost line to the structure on the surface. Most of the entire length of the pier embedded in frost susceptible soil will be vulnerable to frost action.
Many examples of concrete moulds are known. However, none of these addresses the problem of being able to resist upward displacement due to frost heave in the surrounding soil. The problem is particularly acute in climates where the footing must be placed at a significant depth below the surface to remain unaffected by frost. One example of the known art is described in U.S. Pat. No. 5,271,203 issued to Nagle on Dec. 21, 1993 and entitled "Support Form For A Setable Material". Nagle recognizes the problems associated with frost heave and compares the advantages of his invention over conventional thin-walled constant diameter moulds, such as the SONATUBE.TM., which he states are vulnerable to tipping and leaning due to lateral forces caused by frost heave in surrounding soil. While the Nagle invention relies upon its conical shape to resist frost heave, it possesses longitudinal ribs that could permit water to collect and freeze therein thus allowing localized frost action to act detrimentally upon the mould.
Furthermore, the dimensions of the Nagle invention, specifically its height to width ratio, approaches unity. Therefore, for deep frost line applications, where the mould would have to be embedded deeply into the soil and remain connected to the above surface supported structure, the resulting mould of the Nagle design would have to be very large. This would result in greater expense and the mould would require a significant volume of setable material to fill it.
An additional disadvantage of the Nagle invention is that it is of a fixed height and cannot be adjusted at the work site to adapt to the variable depth of excavations. Furthermore, the Nagle invention does not possess anchoring means to prevent the mould from shifting as the concrete is poured. Furthermore, if the Nagle invention is left exposed to the elements for several days before the setable material is poured, there are no means to anchor the Nagle invention to the ground to prevent wind and rain forces from displacing the Nagle invention.